A multi-media presentation is generally presented at its recording rate so that the movement in video and the sound of audio are natural. However, studies indicate that people can perceive and understand audio information at playback rates much higher rates, e.g., up to three or more times higher than the normal speaking rate, and receiving audio information at a rate higher than the normal speaking rate provides a considerable time savings to the user of a presentation.
Simply speeding up the playback rate of an audio signal, e.g., increasing the rate of samples played from a digital audio signal, is undesirable because the increase in playback rate changes the pitch of the audio, which makes the information more difficult to listen to and understand. Accordingly, time-scaled audio techniques have been developed that increase the information transfer rate of audio information without raising the pitch of the audio signal. A continuously variable signal processing scheme for digital audio signals is described in U.S. patent application Ser. No. 09/626,046, entitled “Continuously Variable Scale Modification of Digital Audio Signals,” filed Jul. 26, 2000, which is hereby incorporated by reference in it entirety.
A desirable user convenience would be the ability to change the rate of information, for example, according to the complexity of the information, the amount of attention the user wants to devote to listening, or the quality of the audio. One technique for changing the audio information rate for playback of digital audio is to correspondingly change the digital data rate that the sender transmits and employ a processor or converter at the receiver that processes or converts the data as required to preserve the pitch of the audio.
The above technique can be difficult to implement in a system conveying information over a network such as a telephone network, a LAN, or the Internet. In particular, a network may lack the capability to change the data rate of transmission from a source to the user as required for the change in audio information rate. Transmitting unprocessed audio data for time scaling at the receiver is inefficient and places an unnecessary burden on the available bandwidth because the process of time scaling with pitch restoration discards much of the transmitted data. Additionally, this technique requires that the receiver have a processor or converter that can maintain the pitch of the audio being played. A hardware converter increases the cost of the receiver's system. Alternatively, a software converter can demand a significant portion of the receiver's available processing power and/or battery power, particularly in portable computers, personal digital assistants (PDAs), and mobile telephones where processing and/or battery power may be limited.
Another common problem for network presentations that include video is the inability of the network to maintain the audio-video presentation at the required rate. Generally, the lack of sufficient network bandwidth causes intermittent breaks or pauses in the audio-video presentation. These breaks in the presentation make the presentation difficult to follow. Alternatively, images in a network presentation can be organized as a linked series of web pages or slides that a user can navigate at the user's rate. However, in some network presentations such as tutorials, exams, or even commercials, the timing, sequence, or synchronization of visual and audible portions of the presentation may be critical to the success of the presentation, and the author or source of the presentation may require control of the sequence or synchronization of the presentation.
Processes and systems are sought that can present a presentation in an ordered and uninterrupted manner and give a user the freedom to select and change an information rate without exceeding the capabilities of a network transferring the information and without requiring the user to have special hardware or a large amount of processing power.